Asset-pipeline strategy for packaged Rails engines. Instead of hooking into the host app's asset pipeline (which forces host apps to have Node.js, esbuild, etc. at deploy time), the engine runs esbuild and Tailwind at gem build time, writing compiled output into `public/<engine>-assets/`. A `Rack::Static` middleware registered in the engine class maps the public path to those files so the host app serves them transparently. The engine's application layout picks compiled vs in-development assets via an 'is packed?' check.